In the semiconductor industry, there is a continuing trend toward higher device densities. To achieve these high densities there have been, and continue to be, efforts toward scaling down device dimensions (e.g., at sub-micron levels) on semiconductor wafers. In order to accomplish such high device packing densities, smaller and smaller features sizes are required. This may include the width and spacing of interconnecting lines, spacing and diameter of contact holes, and the surface geometry, such as corners and edges, of various features. The dimensions of and between such small features can be referred to as critical dimensions (CDs).
The process of manufacturing semiconductors, or integrated circuits (commonly called ICs, or chips), typically consists of more than a hundred steps, during which hundreds of copies of an integrated circuit may be formed on a single wafer. Each step can affect the CDs of the ICs. Generally, the manufacturing process involves creating several patterned layers on and into the substrate that ultimately forms the complete integrated circuit. This layering process creates electrically active regions in and on the semiconductor wafer surface.
The requirement of small features with close spacing between adjacent features requires sophisticated manufacturing techniques, including high-resolution photolithographic processes, and controlling post development etch trim processes. Fabricating a semiconductor using such sophisticated lithography techniques may involve a series of steps including cleaning, thermal oxidation or deposition, masking, developing, etching, baking and doping. In general, lithography refers to processes for pattern transfer between various media. It is a technique used for integrated circuit fabrication in which a silicon slice, the wafer, is coated uniformly with a radiation-sensitive film, the photoresist. The photoresist coated substrate is baked to evaporate any solvent in the photoresist composition and to fix the photoresist coating onto the substrate. The baked coated surface of the substrate is next subjected to selective radiation using a mask; that is, a mask is employed to effect an image-wise exposure to radiation.
The mask permits radiation to contact certain areas of the photoresist and prevents radiation from contacting other areas of the photoresist. This selective radiation exposure causes a chemical transformation in the exposed areas of the photoresist coated surface. Types of radiation commonly used in microlithographic processes include visible light, ultraviolet (UV) light and electron beam radiant energy. After selective exposure, the photoresist coated substrate is treated with a developer solution to dissolve and remove either the radiation-exposed or the unexposed areas of the photoresist (depending upon whether a positive photoresist or a negative photoresist is utilized) resulting in a patterned or developed photoresist.
The patterned photoresist may be used in subsequent semiconductor processing such as an etch process in order to transfer its image to underlying semiconductor material layers. Examples of material layers include dielectric layers, conductive layers, and the like. When the image transfer is completed, some photoresist material may undesirably remain on the material layer. Conventional diagnostic methods involved cleaving the wafer in order to obtain information regarding the remaining photoresist material after the etch process. Thus, the wafer was wasted resulting in higher production costs and time delays in manufacturing.